The present invention relates to a plasma technique; and, more particularly, to a method and an apparatus, for use in a display system such as a TV plasma video module employing an AC-type plasma display panel, for driving an AC-type plasma display panel capable of displaying a gray level.
A plasma display panel (referred to as xe2x80x9cPDPxe2x80x9d hereinafter) is a device which displays letters or pictures by using light emitted from plasma generated during gaseous discharge. The PDP is classified into a DC-type and an AC-type depending on a driving method for providing electric field thereto in order to make the plasma.
Since the PDP has advantageous characteristics such as large screen size more than 40 inches, ability to display full-color images and wide viewing angle compared with other flat panel devices, it results in a rapid increase in its application area such a next generation HDTV capable of hanging on the wall and a multimedia display apparatus combining a TV and a personal computer.
There are several methods for driving the AC-type PDP. One of the methods is disclosed in U.S. Pat. No. 5,541,618, assigned to Fujitsu Limited. An address display period separated (ADS) sub-field method disclosed in same will be illustrated hereinafter.
In accordance with the above patent, one image frame is divided into n number of subframes. Each of the subframes includes: an addressing period subsequently providing scan pulses to all scan electrodes in order to indicate cells to be lit; and a display period having a predetermined sustain pulses and concurrently applying sustain pulses to all the scan electrodes, wherein a number of the sustain pulses is predetermined differently for each subframe.
As shown above, the scan pulses are continuously provided onto all the scan electrodes and address pulses are applied onto data electrodes in response to picture data to be displayed. However, according to the ADS sub-field method, since every subframe should have an addressing period for addressing all the scan lines, the display period is relatively shortened. Therefore, the brightness of an image may be decreased.
For example, in order to prevent users from feeling flickers on the screen, the time for controlling illumination of one frame should be limited about {fraction (1/60)} sec or less, namely 16.67 ms. In NTSC system having 480 scan lines, if one image frame is divided into 8 number of subframes, it takes about 11 to 12 ms in addressing one image frame. Because the remaining time for the display period which TV viewer can substantially recognize the image is only 5 to 6 ms, the efficiency becomes only 30% and the brightness of the image is reduced. However, if increasing frequency of sustain pulse in order to compensate the brightness reduction, power consumption is increased and reliability of driving is also decreased.
In particular, in case of HDTV having 1024 scan lines, because it takes about 24 to 25 ms in addressing one image frame, there is no the remaining time for the display period. As a result, the TV viewer cannot recognize the image. Also, since pixels corresponding to scan electrodes are continuously selected for an addressing period, the reliability of driving is reduced by a result of static delay effect which occurs in discharge firing.
There have been proposed another AC-type PDP driving method for providing a gradation of the display brightness, such as the article by Nakamura A. O. xe2x80x9cDrive for 40-in.-Diagonal Full-Color as Plasma Displayxe2x80x9d SID 95 DIGEST pp. 807-810. According to the above method, one image frame is divided with time into n number of subframes which of each have a predetermined number of sustain pulses, each subframe includes a single display period for applying a predetermined number of sustain pulses to all the scan electrodes and an addressing period in which primary discharges is simultaneously created in pixels corresponding to scanning electrode group, thereafter scanning pulses are sequentially formed on all scanning electrodes of this group, similarly, formation of primary discharge and scanning pulse are accomplished for other groups of scanning electrodes.
Problem in the above method disclosed in xe2x80x9cSID 95 DIGESTxe2x80x9d is in that since each subframe should has a addressing period for all scan electrodes, a display period for sustaining an image frame is inevitably reduced, consequently brightness of an image is reduced. In this case, increasing frequency of sustain pulse in order to partially compensate the brightness reduction may causes increase of power consumption and reduction of driving reliability.
Another method for displaying a picture half-brightness (gray scale) is disclosed in U.S. Pat. No. 3,906,290 by Koichiro K. et al. A halftone picture display can be achieved according to two methods, the first being that the mean brightness of the picture element or luminescent dot be made proportional to the turn-on period. The second method is that the mean brightness of the picture element or luminescent dot for the turn-on period be made proportional to the frequency of the sustaining voltage.
Several embodiments are disclosed which incorporate one or both of the foregoing principles to achieve a halftone display.
However, in the above method, there is the fact that the image sharpness and the brightness are reduced. To achieve an image of good quality, the number of subelement in a pixel should be larger, their brightness should be differently set.
Furthermore, according to the above method by Koichiro K. et al., one image frame is divided into n number of subframes, each subframe having a predetermined number of the sustain pulses. Here, scan pulses are provided onto scan electrodes and address pulses are applied onto data electrodes in response to picture data to be displayed.
To realize above method in an AC-type PDP driving circuit, it is necessary to have a plurality of multi-discharge shift registers on logic inputs of scanning pulse drive with complicated logic circuit of connection of their outputs, and it reduces reliability of driving and also rises cost of the device.
Also, there is another driving method of the AC-type PDP for displaying grey level gradation which is disclosed in EP patent No. 0,488,326A2 and developed by NEC Corporation in Japan. According to the driving method of NEC, one field is divided into n number of subfields, all of the second to last subfields have equal period T""s, and the first subfield has period 2T""s. All subfields also have different light emission periods, namely Txe2x80x2, Txe2x80x2/2, Txe2x80x2/4, Txe2x80x2/8, . . . , respectively.
According to this method, although the brightness of an image becomes about 78.8%, since the light emission periods of some subframes have relatively small periods and all pixels corresponding to given scanning electrode are in xe2x80x9coffxe2x80x9d states, the efficiency of an image frame used for displaying cannot be increased more than 78.8%.
It is, therefore, a object of the present invention to provide a gray level display AC-type PDP driving method capable of achieving high sharpness of an image, high brightness and improved reliability by eliminating the before-mentioned problems.
In accordance with one aspect of the present invention, a method for driving an AC-type plasma display panel comprising two substrates separated from each other, display electrodes and scan electrodes disposed on one of said two substrates in parallel, a plurality of display lines consisting of one scan electrode and one or more display electrodes, a dielectric layer covering the display and the scan electrodes, data electrodes disposed on the other of said two substrates, substantially orthogonal to said display lines, a number of pixels formed on crossing points of a display line and a data electrode, spacers formed on one or both of said substrates to partition said pixels, and gas filled in a space between the two substrates, said method comprising the steps of: (a) dividing a single image frame into n number of subframes, each of the subframes having predetermined number of sustaining pulses; (b) selecting display lines whose number is identical to the number of said divided subframes, assigning specific subframes to said selected display lines, sequentially providing scanning pulses having different phases on the scan electrodes of said selected display lines and at the same time applying addressing pulses on is said data electrodes in order to designate pixels to be displayed, and alternately supplying the predetermined number of sustaining pulses onto the selected scan electrodes and said commonly connected display electrodes, to thereby display said assigned subframes for each of said selected display lines; (c) shifting by one or more than display lines from each of said selected display lines, and (d) repeating said shifting of step (c) and displaying of said assigned subframes for selected display lines of step (b) until each of said divided subframes is displayed for all the display lines, to thereby display a image frame.
In accordance with another aspect of the present invention, there is provided a method for driving an AC-type plasma display panel capable of displaying gray levels of an image frame which is divided into n number of subframes, each subframe having predetermined sustain periods, wherein, for each subframe, scan pulses are provided onto selected scan electrodes and addressing pulses are supplied onto data electrodes in response to display information, comprising: the number of sustain pulses, included in two adjacent subframes among the subframes, determined as:
Rxe2x89xa72S/(n+2)
wherein R is the number of sustain pulses; S represents the total number of sustain pulses within the image frame; and n depicts the number of the subframes, the number of sustain pulses in a subframe being of an odd number.